Light-emitting diode and method for fabrication thereof

ABSTRACT

A transparent-substrate light-emitting diode ( 10 ) has a light-emitting layer ( 133 ) made of a compound semiconductor, wherein the area (A) of a light-extracting surface having formed thereon a first electrode ( 15 ) and a second electrode ( 16 ) differing in polarity from the first electrode ( 15 ), the area (B) of a light-emitting layer ( 133 ) formed as approximating to the light-extracting surface and the area (C) of the back surface of a light-emitting diode falling on the side opposite the side for forming the first electrode ( 15 ) and the second electrode ( 16 ) are so related as to satisfy the relation of A&gt;C&gt;B. The light-emitting diode ( 10 ) of this invention, owing to the relation of the area of the light-emitting layer ( 133 ) and the area of the back surface ( 23 ) of the transparent substrate and the optimization of the shape of a side face of the transparent substrate ( 14 ), exhibits high brightness and high exoergic property never attained heretofore and fits use with an electric current of high degree.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 12/158,914filed Oct. 7, 2008, which is a 371 of PCT/JP2006/326299, filed Dec. 22,2006, and claiming priority from Provisional Application Nos.60/754,894, filed Dec. 30, 2005, 60/754,895, filed Dec. 30, 2005, and60/754,320, filed Dec. 29, 2005, and Japanese Patent Application Nos. JP2005-369334, JP 2005-369620, and JP 2005-369996, all filed Dec. 22,2005. The above-noted applications are incorporated herein by referencein their entireties.

TECHNICAL FIELD

This invention relates to a transparent-substrate light-emitting diodeprovided with a light-emitting layer made of a compound semiconductor,and furnished with a light-extracting surface having formed thereon afirst electrode and a second electrode possessing polarity differentfrom the first electrode. More particularly, this invention relates to alight-emitting diode excelling in exoergic property and exhibiting highbrightness and to a method for the fabrication thereof.

BACKGROUND ART

With the object of imparting high brightness to light-emitting diodes,the method of relying on the shape of a device for enhancement of thelight-extracting efficiency has been in use heretofore. In the devicestructure that has electrodes each formed on the first surface and theback surface of a semiconductor light-emitting diode, for example, themethod for imparting high brightness by the shape of a side face hasbeen proposed (refer to JP-B SHO 63-28508, U.S. Pat. No. 6,229,160 andJP-A HEI 3-227078, for example).

As a Light-Emitting Diode (LED) capable of emitting a visible light in ared, orange, yellow or yellowish green color, compound semiconductorLEDs provided with a light-emitting layer made ofaluminum-gallium-indium phosphide ((Al_(X)Ga_(1-X))_(Y)In_(1-Y) P; inwhich 0≦X≦1 and 0<Y≦1) have been known heretofore. In the LEDs of thiskind, the light-emitting part provided with the light-emitting layerthat is made of (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; in which 0≦X≦1 and 0<Y≦1)is generally impervious optically to the light emitted from thelight-emitting layer and is mechanically formed on the substratematerial, such as gallium arsenide (GaAs), which has no appreciablestrength.

Recently, for the purpose of obtaining a visible LED exhibiting as highbrightness as possible and with the object of further enhancing themechanical strength of a device as well, therefore, the techniques forconfiguring a junction-type LED by removing an impervious substratematerial, such as GaAs, and thereafter joining by way of innovation abacking layer made of a transparent material capable of transmittingemitted light and excellent in mechanical strength more than ever havebeen disclosed (refer to Japanese Patent No. 3230638, JP-A HEI 6-302857,JP-A 2002-246640, Japanese Patent No. 2588849 and JP-A SHO 58-34985, forexample).

Then, for the purpose of obtaining a visible LED of high brightness, themethod that enhances the light-extracting efficiency by dint of theshape of device has been finding acceptance. As one example, in thedevice structure having electrodes formed each on the first surface andthe back surface of a semiconductor light-emitting diode, the techniquethat relies on the side structure for enhancing high brightness has beendisclosed (refer to U.S. Pat. No. 6,229,160 cited above and JP-A SHO58-34985, for example).

The conventional technique has proposed numerous shapes for devices soconfigured as to have electrodes formed each on the first surface andthe back surface of a light-emitting diode but has not studied theexoergic property exhibited by such a device when the device is usedwith an electric current of high level. Particularly, the light-emittingdiode containing an AlGaInP and gallium nitride-based light-emittinglayer provided on a light-extracting surface thereof with two electrodesis inferior in exoergic property to the device structure havingelectrodes disposed on the back surface because it has no electrodedisposed on the back surface. It is known that the deficiency of theexoergic property results in elevating the temperature of thelight-emitting layer, lowering the light-emitting efficiency anddegrading the brightness.

The structure of the device using a transparent-substrate AlGaInPlight-emitting layer and having two electrodes formed on alight-extracting surface entails such problems as complicating theshape, failing to optimize the electrode disposition, the side facecondition and the back surfaces of the light-emitting layer and deviceand not acquiring high brightness and sufficient exoergic property.

While the junction-type LED has enabled provision of an LED of highbrightness, the need for an LED exhibiting still higher brightness haspersisted. This invention has been proposed in view of the problemsmentioned above. In a light-emitting diode possessing two electrodes ona light-extracting surface, this invention is aimed at providing alight-emitting diode that excels in exoergic property, exhibits a highlight-extracting efficiency and possesses high brightness.

It is clear even from the conventional technique that the shape of theside face of a light-emitting diode is related to the extraction oflight from the diode. In the structure having a light-emitting surfacein the upper part, when the angle of inclination is increased for thepurpose of rendering the effect of the shape of the side faceconspicuous, the increase results in decreasing the area of the backsurface, lowering the exoergic property and degrading the property ofbrightness in the region of high degree of electric current. When thelight-emitting layer is made smaller and the area of the back surface ismade larger for the purpose of enhancing the exoergic property, theproblem of cost ensues because the expensive light-emitting layer incursa great loss. When the light-emitting layer is approximated to the backsurface, the structure that possesses two electrodes on one surfacecannot be assembled by the ordinary wire bonding process.

The present inventors, as a result of a comprehensive study pursued onthe shape and the back surface of a light-emitting diode, havediscovered that the structure and area of the back surface, the area ofthe light-emitting layer, the shape of the side face and the coarseningof the back surface dictate an important consideration and eventuallyperfected this invention by finding out the optimum device structure andthe stable method of fabrication. Specifically, for the purpose ofaccomplishing the object described above, this invention has beenaccomplished.

DISCLOSURE OF THE INVENTION

The first aspect of this invention consists in a light-emitting diodepossessing a transparent substrate and a light-emitting layer made of acompound semiconductor, wherein an area (A) of a light-extractingsurface having formed thereon a first electrode and a second electrodediffering in polarity from the first electrode, an area (B) of thelight-emitting layer formed as approximating to the light-extractingsurface and an area (C) of a back surface of the light-emitting diodefalling on a side opposite a side for forming the first electrode andthe second electrode are so related as to satisfy a relation of formula(1).A>C>B  (1)

The second aspect of this invention includes the configuration of thefirst aspect, wherein the light-emitting layer has a composition of theformula (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; wherein 0≦X≦1 and 0<Y≦1, and thetransparent substrate has a heat transfer coefficient of 100 W/m·k ormore.

The third aspect of this invention includes the configuration of thefirst or second aspect, wherein the transparent substrate possesses aside face comprising a first side face approximating to thelight-emitting layer and a second side face approximating to a backsurface of the transparent substrate and wherein the first side face hasan angle of inclination smaller than an angle of inclination of thesecond side face.

The fourth aspect of this invention includes the configuration of thethird aspect, wherein the first side face is perpendicular and thesecond side face is inclined.

The fifth aspect of this invention consists in a light-emitting diodecomprising a compound semiconductor layer furnished with alight-emitting part containing a light-emitting layer having acomposition of formula (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; in which 0≦X≦1 and0<Y≦1, a transparent substrate having the compound semiconductor layerjoined thereto and a main light-extracting surface having formed thereona first electrode and a second electrode differing in polarity from thefirst electrode, wherein the second electrode is formed on the compoundsemiconductor layer exposed to a side opposite the first electrode andthe transparent substrate has a side face comprising a first side faceroughly perpendicular to the light-emitting surface of thelight-emitting layer on a side approximating to the light-emitting layerand a second side face inclined to the light-emitting surface on a sidedistant from the light-emitting layer.

The sixth aspect of this invention consists in a light-emitting diodecomprising a compound semiconductor layer furnished with alight-emitting part containing a light-emitting layer having acomposition of formula (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; in which 0≦X≦1 and0<Y≦1, a transparent substrate having the compound semiconductor layerjoined thereto and a main light-extracting surface having formed thereona first electrode and a second electrode differing in polarity from thefirst electrode, wherein the second electrode is formed at a cornerposition on the compound semiconductor layer exposed to a side oppositethe first electrode and the transparent substrate has a side facecomprising a first side face roughly perpendicular to the light-emittingsurface of the light-emitting layer on a side approximating to thelight-emitting layer and a second side face inclined to thelight-emitting surface on a side distant from the light-emitting layer.

The seventh aspect of this invention includes the configuration of thethird or fourth aspect, wherein the angle of inclination of the secondside face is 10 degrees or more and 30 degrees or less.

The eighth aspect of this invention includes the configuration of thethird or fourth aspect, wherein the angle of inclination of the secondside face is 10 degrees or more and 20 degrees or less.

The ninth aspect of this invention includes the configuration of thefifth or sixth aspect, wherein the second side face and a surfaceparallel to the light-emitting surface form therebetween an angle in arange of 55 degrees˜80 degrees.

The tenth aspect of this invention includes the configuration of thethird or fourth aspect, wherein the first side face has a length of 50μm or more and 100 μm or less and the second side face has a length of100 μm or more and 250 μm or less.

The eleventh aspect of this invention includes the configuration of thefifth or sixth aspect, wherein the first side face has a length in arange of 30 μm˜100 μm.

The twelfth aspect of this invention includes the configuration of thefirst, fifth or sixth aspect, wherein the transparent substrate is madeof gallium phosphide (GaP).

The thirteenth aspect of this invention includes the configuration ofthe fifth or sixth aspect, wherein the transparent substrate is ann-type GaP single crystal in substance and has a surface orientation of(100) or (111).

The fourteenth aspect of this invention includes the configuration ofthe fifth or sixth aspect mentioned above, wherein the transparentsubstrate has a thickness in a range of 50 μm ˜300 μm.

The fifteenth aspect of this invention includes the configuration of thefifth or sixth aspect, wherein the transparent substrate is made ofsilicon carbide (SiC).

The sixteenth aspect of this invention includes the configuration of thefirst aspect, wherein the transparent substrate has a back surface thatis a coarsened surface capable of scattering light.

The seventeenth aspect of this invention includes the configuration ofthe first aspect, wherein the transparent substrate has a back surfacehaving a metal film formed thereon.

The eighteenth aspect of this invention includes the configuration ofthe seventeenth aspect, wherein the metal film on the back surface ofthe transparent substrate contains a metal having a melting point of400° C. or less.

The nineteenth aspect of this invention includes the configuration ofthe seventeenth aspect, wherein the metal film is made of an AuSn alloy.

The twentieth aspect of this invention includes the configuration of thefirst aspect, wherein the light-emitting diode is used with an electricpower of 1.5 W or more and the area of the back surface thereof is 0.6mm² or more.

The twenty-first aspect of this invention includes the configuration ofthe sixteenth aspect, wherein the transparent substrate is a GaPsubstrate and the back surface thereof results from treatment of the GaPsubstrate with hydrochloric acid.

The twenty-second aspect of this invention includes the configuration ofthe third aspect, wherein the first and second side faces of thetransparent substrate are those formed by the dicing method.

The twenty-third aspect of this invention includes the configuration ofthe fifth aspect, wherein the second electrode has a periphery thereofencircled with a semiconductor layer.

The twenty-fourth aspect of this invention includes the configuration ofthe sixth aspect, wherein the second electrode is positioned above aninclined structure of the second side face.

The twenty-fifth aspect of this invention includes the configuration ofthe fifth aspect, wherein the first electrode has a shape of a lattice.

The twenty-sixth aspect of this invention includes the configuration ofthe fifth or sixth aspect, wherein the first electrode comprises a padelectrode and a linear electrode having a width of 10 μm or less.

The twenty-seventh aspect of this invention includes the configurationof the fifth or sixth aspect, wherein the light-emitting part contains aGaP layer and the second electrode is formed on the GaP layer.

The twenty-eighth aspect of this invention includes the configuration ofthe fifth or sixth aspect, wherein the first electrode possesses ann-type polarity and the second electrode possesses a p-type polarity.

The twenty-ninth aspect of this invention includes the configuration ofthe fifth or sixth aspect, wherein the inclined second face of thetransparent substrate has coarseness.

The thirtieth aspect of this invention consists in a method for thefabrication of a light-emitting diode, comprising the steps of forming alight-emitting part containing a light-emitting layer having acomposition of formula (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; in which 0≦X≦1 and0<Y≦1, subsequently causing a compound semiconductor layer containingthe light-emitting part to be joined to a transparent substrate, causinga first electrode attached to a main light-emitting surface on a sideopposite the transparent substrate and a second electrode differing inpolarity from the first electrode to be formed on an exposed part of thecompound semiconductor layer in such a manner that the second electrodemay be disposed on a side opposite the first electrode, and allowingside faces of the transparent substrate to form a first side faceroughly perpendicular to the light-emitting surface of thelight-emitting layer on a side approximating to the light-emitting layerand a second side face inclined to the light-emitting surface on a sidedistant from the light-emitting layer by a dicing method.

The thirty-first aspect of this invention consists in a method for thefabrication of a light-emitting diode, comprising the steps of forming alight-emitting part containing a light-emitting layer having acomposition of formula (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; in which 0≦X≦1 and0<Y≦1, subsequently causing a compound semiconductor layer containingthe light-emitting part to be joined to a transparent substrate, causinga first electrode attached to a main light-emitting surface on a sideopposite the transparent substrate and a second electrode differing inpolarity from the first electrode to be formed at a corner position onan exposed part of the semiconductor layer in such a manner that thesecond electrode may be disposed on a side opposite the first electrode,and allowing side faces of the transparent substrate to form a firstside face roughly perpendicular to the light-emitting surface of thelight-emitting layer on a side approximating to the light-emitting layerand a second side face inclined to the light-emitting surface on a sidedistant from the light-emitting layer by a dicing method.

The thirty-second aspect of this invention includes the configuration ofthe thirtieth or thirty-first aspect, wherein the first side face isformed by a scribe and break method.

The thirty-third aspect of this invention includes the configuration ofthe thirtieth or thirty-first aspect, wherein the first side face isformed by a dicing method.

According to this invention described above, since atransparent-substrate light-emitting diode possessing a light-emittinglayer made of a compound semiconductor has the relation of the area ofthe light-emitting layer and the area of the back surface of thetransparent substrate and the condition of the side face of thetransparent substrate optimized, it is made possible to provide alight-emitting diode that possesses such high brightness as has neverbeen attained heretofore, exhibits a high exoergic property and suitsuse of a high degree of electric current.

Further, according to this invention, the transparent-substratelight-emitting diode possessing a light-emitting layer made of acompound semiconductor is enabled to have the disposition of electrodesand the shape of chips optimized. This invention, therefore, is capableof providing a light-emitting diode that has the efficiency ofextracting light from the light-emitting part enhanced to a level notattainable heretofore, exhibits high brightness, suppresses theoperation voltage and possesses high reliability.

The above and other objects, characteristic features and advantages ofthe present invention will become apparent to those skilled in the artfrom the description to be given herein below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a semiconductor light-emitting diode10 of Example 1.

FIG. 2 is a schematic cross section taken through FIG. 1 along lineII-II.

FIG. 3 is a schematic view illustrating a cross-sectional structure of asemiconductor epitaxial stacked structure in Example 1.

FIG. 4 is a schematic cross section illustrating a structure having asubstrate joined to the semiconductor epitaxial stacked structure ofFIG. 3.

FIG. 5 is a schematic cross section of a semiconductor light-emittingdiode 10 of Example 2.

FIG. 6 is a schematic cross section of a semiconductor light-emittingdiode A of Comparative Example 1.

FIG. 7 is a schematic cross section of a semiconductor light-emittingdiode B of Comparative Example 2.

FIG. 8 is a schematic plan view of a semiconductor light-emitting diodelamp 1 using the semiconductor light-emitting diode 10 of Example 1 as aLED chip 42.

FIG. 9 is a schematic cross section of the semiconductor light-emittingdiode lamp 1 taken through FIG. 8 along line IX-IX.

FIG. 10 is a schematic plan view of a semiconductor light-emitting diode10 of Example 3.

FIG. 11 is a schematic cross section taken through FIG. 10 along lineXI-XI.

FIG. 12 is a schematic cross section of the layer structure of asemiconductor epitaxial stacked structure used in the semiconductorlight-emitting diode 10 of Example 3.

FIG. 13 is a schematic cross section illustrating a structure having aGaP substrate 14 joined to the semiconductor epitaxial stacked structureof FIG. 12.

FIG. 14 is a schematic plan view of a semiconductor light-emitting diodelamp 1 using the semiconductor light-emitting diode 10 of Example 3 asan LED chip 42.

FIG. 15 is a schematic cross section taken through FIG. 14 along lineXV-XV.

FIG. 16 is a schematic plan view of a semiconductor light-emitting diode10 of Example 4.

FIG. 17 is a schematic cross section taken through FIG. 16 alone lineXVII-XVII.

FIG. 18 is a schematic plan view of a semiconductor light-emitting diodeC of Comparative Example 3.

FIG. 19 is a schematic cross section taken through FIG. 18 along lineXIX-XIX.

BEST MODE FOR CARRYING OUT THE INVENTION

The light-emitting diode of this invention possesses a light-emittinglayer made of a compound semiconductor. Though known light-emittinglayers, such as GaAlAs-based, InGaN-based and AlInGaP-basedlight-emitting layers, are available as the light-emitting layermentioned above, particularly InGaN-based and AlInGaP-basedlight-emitting layers that have a thin epitaxial layer are easy tofabricate. These light-emitting parts are effective for wavelengths in abroad range extended from the ultraviolet to the infrared wavebands.

The light-emitting diode of this invention prefers to comprise alight-emitting part resulting from stacking a clad layer, a contactlayer and the like besides the light-emitting layer.

The light-emitting part contemplated by this invention prefers toconsist of a compound semiconductor stacked structure containing alight-emitting layer made of (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; (0≦X≦1,0<Y≦1). In this case, the light-emitting layer can be formed of(Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; (0≦X≦1, 0<Y≦1) of either of theconduction types, n-type and p-type. Though the light-emitting layer maybe in either of the structures, i.e. a Single Quantum Well (SQW)structure and a Multi-Quantum Well (MQW) structure, it prefers to havethe MQW structure for the purpose of obtaining light emission excellingin monochromaticity. The composition of (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P;(0≦X≦1, 0<Y≦1) of which a barrier layer and a well layer possessing aQuantum Well (QW) structure are formed is so decided that the quantumlevel fated to form an expected light-emitting wavelength may be formedwithin the well layer.

Most advantageously for the sake of securing light emission of highintensity, the light-emitting part prefers to have the so-called DoubleHetero (DH) structure that comprises the light-emitting layer and cladlayers disposed as opposed to each other at the opposite sides of thelight-emitting layer for the purpose of “entrapping” in thelight-emitting layer the carrier and the light emission destined tobring about radiation recombination. The clad layer prefers to be formedof a semiconductor material possessing a wider forbidden band and ahigher refractive index rather than the composition of(Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; (0≦X≦1, 0<Y≦1) of which thelight-emitting layer is formed. As regards the light-emitting layerformed of Al_(0.4)Ga_(0.6))_(0.5)In_(0.5)P and enabled to emit ayellowish green color having a wavelength of about 570 nm, for example,the clad layer is formed of (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P (Y.Hosokawa et al., J. Crystal Growth, 221 (2000), 652-656). It ispermissible to interpose between the light-emitting layer and the cladlayer an intermediate layer adapted to change moderately thediscontinuity of band between the two layers. In this case, theintermediate layer prefers to be formed of a semiconductor materialpossessing a forbidden band width intermediate between thelight-emitting layer and the clad layer.

As means to form the component layers of the light-emitting part, theMetalOrganic Chemical Vapor Deposition (MOCVD) means, the Molecular BeamEpitaxial (MBE) means and the Liquid Phase Epitaxial (LPE) means may becited.

The light-emitting diode of this invention is a so-calledtransparent-substrate light-emitting diode that is provided on the sideopposite a light-extracting surface with a transparent substrate. Thisinvention, therefore, needs to join a transparent substrate to alight-emitting part furnished with a light-emitting layer. Thetransparent substrate is formed of a material possessing strengthsufficient for mechanically supporting the light-emitting part,imparting a large width to the forbidden band capable of transmittingthe light emitted from the light-emitting part, and exhibitingtransparency to the optical wavelength. For example, it may be formed ofa Group III-V compound semiconductor crystal, such as gallium phosphide(GaP), aluminum-gallium arsenide (AlGaAs) or gallium nitride (GaN), aGroup II-VI compound semiconductor crystal, such as zinc sulfide (ZnS)or zinc selenide (ZnSe), a Group IV semiconductor crystal, such ashexagonal or cubic silicon carbide (SiC), or zinc oxide, sapphire oralumina. Particularly, GaP and SiC are usable preferably among othermaterials cited above. GaP is mass-produced in the form of a singlecrystal and excels in workability. The thermal conductivity of GaP is110 W/m·K. Though GaP is allowed to adopt as its principal plane for thepurpose of processing any of ordinary surface orientations, such as(111) face and (100) face, it prefers to use as the principal plane the(111) face that is easily coarsened. SiC, in spite of weakness inincurring difficulty of processing, is mass-produced in the form of asingle crystal and exhibits thermal conductivity of 167 W/m·K and,therefore, proves to be the most suitable material in terms of radiationof heat.

The transparent substrate prefers to have an approximate thickness of 50μm or more in order to support the light-emitting part with mechanicallysufficient strength. It further prefers to keep the thickness fromexceeding about 300 μm in order that the transparent substratesubsequent to joining may undergo mechanical processing easily. In thecompound semiconductor LED furnished with the light-emitting layer madeof (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P (0≦X≦1, 0<Y≦1), it is most appropriateto form the transparent substrate of n-type GaP single crystal having athickness of 50 μm or more and about 300 μm or less.

In the case of joining a transparent substrate made of gallium phosphide(GaP) to the uppermost surface layer of a light-emitting part, forexample, the choice of forming the uppermost surface layer of thelight-emitting part with a Group III-V compound semiconductor materialthat differs in lattice constant from the other Group III-V compoundsemiconductor component layers of the light-emitting part enablesmanifestation of the function of allaying the stress exerted on thelight-emitting part while the transparent substrate is joined thereto.The use of this material results in preventing the light-emitting layerfrom sustaining damage during the course of joining and contributing,for example, to stable provision of a compound semiconductor LED capableof emitting light of an expected wavelength. The uppermost surface layerof the light-emitting part prefers to have a thickness of 0.5 μm or morefor the purpose of sufficiently allaying the stress exerted on thelight-emitting part while the transparent substrate is joined thereto.If the uppermost surface layer is given an unduly large thickness, theexcess will result in inevitably exerting stress on the light-emittinglayer during the course of forming the uppermost surface layer becauseof the difference in lattice constant from the other component layers ofthe light-emitting part For the sake of avoiding this mishap, it isproper to give the uppermost surface layer a thickness of 20 μm or less.

Particularly, when gallium phosphide (GaP) is selected for a transparentsubstrate that is convenient for the purpose of transmitting to theexterior the light emitted from a light-emitting layer made of(Al_(X)Ga_(1-X))_(Y)In_(1-Y)P (0≦X≦1, 0<Y≦1), the manufacture of theuppermost layer of the light-emitting part with a semiconductor materialcontaining gallium (Ga) and phosphorus (P) as component elements andcontaining Ga more than P enables formation of strong joining. It isparticularly appropriate to form the uppermost layer of Ga_(X)P_(1-X)(0.5<X<0.7), a nonstoichiometric composition.

The surface of the transparent substrate about to be joined and thesurface of the uppermost layer of the light-emitting part are surfacesformed of single crystal and these surfaces prefer to have an identicalsurface orientation. The surfaces both prefer to have a (100) face or a(111) face invariably. For the purpose of obtaining an uppermost layerof a light-emitting part having a (100) face or a (111) face for thesurface thereof, it suffices to use a substrate having a (100) face or a(111) face for the surface thereof in forming the uppermost layer of thelight-emitting part on a substrate. When a gallium arsenide (GaAs)single crystal having a (100) face as the surface thereof is used as asubstrate, for example, an uppermost layer of a light-emitting parthaving a (100) face as the surface thereof can be formed.

Particularly strong joining is accomplished when the surface of thetransparent substrate or the uppermost layer of the light-emitting partto which the substrate is joined is so flat as to be expressed by aroot-mean-square value (rms) of 0.3 nm or less. The surface of thisflatness can be obtained, for example, by the Chemical MechanicalPolishing (CMP) means that uses an abrasive agent containing a siliconcarbide (SiC)-based fine powder or a cerium (Ce) fine powder. When thesurface resulting from the chemical mechanical polishing is furthertreated with an acid solution or an alkali solution, this treatmentenables further enhancement of the flatness of surface and contributesto the acquisition of a clean surface in consequence of the removal offoreign matter and contaminant suffered to adhere to the surface duringthe course of polishing.

The uppermost layer of the transparent substrate or the light-emittingpart is subjected to the joining in a vacuum of 1×10⁻² Pa or less andmore preferably 1×10⁻³ Pa or less. Particularly by mutually joining thepolished flat surfaces as described above, it is made possible to formstrong joining. In joining these two surfaces mutually, it is necessarythat the surfaces about to be joined be activated by irradiation with anatomic beam or an ion beam possessing energy of 50 eV or more. The term“activation” refers to the creation of a surface in a clean stateresulting from removing an impurity layer and a contaminated layercontaining oxide film and carbon and existing on the surfaces beingjoined. When this irradiation is performed on the surface of either ofthe transparent substrate or the component layer of the light-emittingpart, the two surfaces are joined strongly and infallibly. When theirradiation is performed on both the surfaces, they can be joined withgreater strength.

As an irradiation species that proves effective in bringing about strongjoining, the beam of hydrogen (H) atom, hydrogen molecule (H₂) orhydrogen ion (proton: H₊) may be cited. By using for the irradiation abeam containing an element existing in the surface region about to bejoined, it is made possible to obtain the joining that excels instrength. When gallium phosphide (GaP) having added zinc (Zn) is usedfor a transparent substrate, for example, the joining can be formedstrongly by irradiating the surfaces about to be joined with an atomicor ion beam containing gallium (Ga), phosphorus (P) or zinc (Zn). Whenthe surface of the transparent substrate or the uppermost layer of thelight-emitting layer has high electric resistance, the irradiation ofthe surface with a beam that mainly contains ions possibly results inelectrifying the surface. Since the joining cannot be formed stronglywhen this electrification of the surface induces an electric repulsion,the activation of the surface by the irradiation with an ion beam ispreferably utilized for activating the surface that excels in electricalconductivity.

In the surface region of a transparent substrate or a component layer ofa light-emitting part, the use of a beam of an inert gas, such as helium(He), neon (Ne), argon (Ar) or krypton (Kr) that is incapable ofexerting a conspicuous change on the composition thereof results infulfilling the activation of the surface stably. Particularly, the useof the beam of argon (Ar) atom (monoatomic molecule) proves to bebeneficial in that it permits the surface to be expeditiously andconveniently activated. Helium (He) has a smaller atomic weight thanargon (Ar) and, therefore, the He beam is at a disadvantage in entailingwaste of time during the activation of the surface about to be joined.Meantime, the use of the beam of krypton (Kr) having a larger atomicweight than argon is at a disadvantage in possibly inflicting damage ofimpact on the surface.

On the occasion of joining the surface of the transparent substrate andthe surface of the uppermost layer of the light-emitting part while thesurfaces are overlapped in an opposed state, an effort to make themechanical pressure over the entire joining surfaces proves to befavorable for strongly joining them. To be specific, the pressurefalling in the range from 5 g·cm⁻² to 100 g·cm⁻² is exerted on thejoining surfaces in the direction perpendicular thereto (vertically).Even when either or both of the transparent substrate and the uppermostlayer of the light-emitting part are warped, this method succeeds ineliminating the warp and effecting the joining with uniform strength.

The transparent substrate and the light-emitting part are joined invacuum of the preferred degree of vacuum mentioned above while either orboth of the surfaces of the transparent substrate and the uppermostlayer of the light-emitting part are kept below 100° C. and preferablybelow 50° C. and more preferably at room temperature. If they are joinedin a high-temperature environment exceeding about 500° C., the excess oftemperature will be at a disadvantage in thermally denaturalizing thelight-emitting layer formed of (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P (0≦X≦1,0<Y≦1) and incorporated in the light-emitting part and consequentlydisrupting stable fabrication of a compound semiconductor LED capable ofemitting light of an expected wavelength.

This invention joins a transparent substrate to the uppermost layer of alight-emitting part so as to set the light-emitting part in amechanically supportable state and subsequently removes the substrateutilized for forming the light-emitting part so as to enhance theefficiency of extracting the emitted light to the exterior andconsequently completes configuration of a compound semiconductor LED ofhigh brightness. Particularly when an optically impervious materialinevitably absorbing the light emitted from the light-emitting layer of(Al_(x)Ga_(1-X))_(Y)In_(1-Y)P (0≦X≦1, 0<Y≦1) is utilized as a substrate,the means to remove the substrate in the manner described above cancontribute to stable fabrication of an LED of high brightness. When alayer such as, for example, a buffer layer that is made of a materialabsorbing the light emitted from the light-emitting layer intervenesbetween the substrate and the light-emitting part, the removal of theintervening layer in combination with the substrate proves to befavorable for imparting high brightness to the LED. The substrate can beremoved by mechanical cutting, grinding, or physical dry or chemical wetetching or by combining these operations. Particularly by the selectiveetching means that utilizes differences in etching speed among materialsof varying quality, it is made possible to achieve selective removal ofthe substrate alone and enable the removal of the substrate withsatisfactory reproducibility and uniformly as well.

This invention is characterized by having a first electrode (of n-type,for example) and a second electrode (of a p-type, for example) bothformed on a main light-extracting surface of a light-emitting diode. Theterm “main light-extracting surface” as used herein refers to thesurface placed opposite a surface on which a transparent substrate ismounted in a light-emitting part. The reason for this inventionconfiguring the electrodes in this way resides in the impartation ofhigh brightness. By adopting this configuration, it is made possible toobviate the necessity of feeding an electric current to the transparentsubstrate being mounted. Consequently, the impartation of highbrightness can be accomplished because a substrate abounding intransmittance can be mounted.

A light-emitting diode according to the first embodiment of thisinvention and a method for the fabrication thereof will be described indetail below by reference to FIG. 1 through FIG. 5.

As regards electrodes, a first electrode and a second electrodediffering in polarity therefrom are formed on a light-extracting surfaceas illustrated in FIG. 2. Both these electrodes possess a structure ableto receive the work of wire bonding. The second electrode is formed byhaving part of a stacked body etched from the surface thereof to below alight-emitting layer and connected to a semiconductor layer or anelectrically conductive transparent substrate.

This transparent substrate is joined on a semiconductor layer 135 asdesignated by a reference numeral 14 in FIG. 4.

The light-emitting diode according to the first embodiment ischaracterized in that the area (A) of a light-extracting surface, thearea (B) of a light-emitting layer and the area (C) of the back surfaceof the light-emitting diode (the surface on the side opposite theelectrode-forming side of a transparent substrate) are in a specificrelation. The light-emitting diode generally has the periphery of thelight-emitting region thereof covered with transparent resin. Sincetransparent resin, such as epoxy resin, has inferior thermal conduction,however, the light-emitting region of the light-emitting diode cannot beexpected to allow radiation of heat. Most of the heat generated in thelight-emitting diode, therefore, is radiated through the substrate of apackage contiguous to the back surface of the light-emitting diode. Thearea (C) of the back surface serving as an exoergic surface, the area(B) of the light-emitting layer constituting a heat-generating surface,and the area (A) of the upper surface of the device functioning as alight-extracting surface have the optimum relation with brightness andheat radiation.

Though the relation of C>A>B proves to be favorable in soleconsideration of the exoergic surface, the impartation of highbrightness cannot be achieved when the light-extracting surface and thelight-emitting layer have small areas. Further, the area of theexpensive epitaxial layer to be removed is so increased as to boost thecost. To obtain high brightness, the area (B) of the light-emittinglayer and area (A) of the light-extracting surface are made maximum,with the side face of the transparent substrate formed as an inclinedface. The light-emitting layer is located near the light-extractingsurface. The heat generated in the light-emitting layer is let loose bybeing diffused in the large area (A) of the light-extracting surface toexpel the heat in the light-emitting layer, smoothly conducted along theinterior of the structure of the light-emitting diode, and eventuallyradiated to the back surface serving as an exoergic surface.

Since it is necessary that the impartation of high brightness bepromoted and the radiation of heat be enhanced as well by inclining theside faces of the transparent substrate, it is favorable to avoiddisposing an inclined face on the side face of the transparent substratenear the light-emitting layer for the purpose of enlarging the area (A)of the light-extracting surface. For the purpose of enabling the heat tobe easily diffused, the semiconductor near the light-emitting layerprefers to have as large a volume as permissible. Thus, the inclinedface is formed on the side face of the transparent substrate near theback surface that is distant from the light-emitting layer. Since theinclined face near the back surface touches a material possessing anexcellent exoergic property, the heat finds ample escape and allows norate-determining degree of heat radiation even when the area (C) of theback surface of the light-emitting diode is slightly smaller than thearea (A) of the light-extracting surface. The conditions that arefavorable for maintaining the balance of areas are shown below.0.95×A>C>0.6×A0.9×A>B>0.7×AC<B>0.8×C∴A>C>B

A light-emitting diode operating with an electric power of 0.5 W or moreis required to possess a high exoergic property and a light-emittingdiode of a large size used with a large electric power of 1.5 W or moreis required to possess a still higher exoergic property. In thelight-emitting diode that is used with such a large electric power asthis, the back surface prefers to possess an area of 0.6 mm² or more.The exoergic effect to be manifested by the light-emitting diode gainsin prominence in accordance as the size of this diode increases.

When the transparent substrate is formed of GaP, it prefers to have theback surface thereof treated with hydrochloric acid. Particularly, themethod that utilizes the face of the surface orientation (111) for thistreatment proves to be favorable.

The light-emitting diode according to the first embodiment is alsocharacterized by the shape of the side face. That is, in the ordinarycase, it is characterized by the fact that at least one of the sidefaces of the transparent substrate is inclined. The transparentsubstrate prefers to possess a first side face 21 and a second side face22 as illustrated in FIG. 2 and FIG. 5. Then, the angle of inclinationof the first side face 21 is smaller than the angle of inclination ofthe second side face 22. In this case, the first side face 21 prefers tohave no (zero) angle of inclination, i.e. to be perpendicular to thetransparent substrate. The angle of inclination of the second side face22, in FIG. 2 and FIG. 5, is indicated by an inclined angle 20 relativeto the perpendiculars of the transparent substrate. The angle ofinclination of the second side face 22 is preferably in the range of 10degrees or more and 30 degrees or less and more preferably in the rangeof 10 degrees or more and 20 degrees or less. The second side face 22may be an inclined face having a fixed angle of inclination, an inclinedface formed in a polygonal shape with a plurality of angles ofinclination or an inclined curved face. When the second side face 22 isformed of a plurality of angles of inclination, the angle of the secondside face 22 is expressed by the arithmetic mean of all the angles ofinclination. In the case of a curved face, the angle of the second sideface 22 is expressed by the angle with a line connecting the startingpoint and the end point of the curved face.

The angle of the side face of the transparent substrate has brightnessand an exoergic property taken into consideration. The light-emittingdiode of the first embodiment wherein the side face of the transparentsubstrate is shaped as described above particularly excels in theproperties manifested in the region of high electric current Though thelargeness of the angle of the side face of the transparent substrate isadvantageous in terms of the extraction of light, the angle in the rangementioned above is most favorable because the addition to this angletends to heighten thermal resistance on account of the proportionatedecrease in the area (C) of the back surface of the light-emittingdiode. Incidentally, the idea of enhancing the efficiency of lightextraction by inclining the side face of the light-emitting diode hasbeen known to the public as described in the documents mentionedearlier.

In the light-emitting diode of the first embodiment, by causing thetransparent substrate to be so formed as to have the first side face 21and the second side face 22 as described above and further causing thefirst side face 21 to acquire a smaller angle of inclination than thesecond side face 22, it is made possible to bring about the effect ofenlarging the area near the light-emitting layer and promoting theradiation of heat and allowing the second side face 22 to heightenbrightness.

Concerning the lengths of the side faces, the length (L) of the firstside face 21 prefers to be 50 μm or more and 100 μm or less and thelength (M) of the second side face 22 prefers to be 100 μm or more and250 μm or less. And the ratio MIL prefers to be in the range from 1 to5.

The first side face 21 and the second side face 22 of the transparentsubstrate of the light-emitting diode can be formed by the dicingmethod. Alternatively, the side faces of the transparent substrate maybe formed by using methods, such as wet etching, dry etching, scribingand laser processing, in combination. Nevertheless, the dicing methodthat excels in the shape controlling property and the productivityproves to be most suitable.

A back face 23 of the transparent substrate of the light-emitting diodemay be formed into a coarsened surface capable of scattering light Theback face 23 of the light-emitting diode is a surface that is connectedto a package resulting form assembling. The connecting face is generallycemented on the package by using an Ag paste having high reflectance orfixed on a metal, such as silver or aluminum, having high reflectancewith a transparent adhesive agent with a view to heightening thebrightness of the light-emitting diode. The back face 23 that is formedof a coarsened surface capable of scattering light contributes to theenhancement of brightness because the light not easily extracted fromthe side face or the upper face can be scattered at angles of reflectioncapable of extracting light. Further, since the back face 23 formed of acoarsened surface capable of scattering light acquires addition to thesurface area, it also manifests the effect of an exoergic surfaceclaimed to facilitate the escape of heat toward the package side.

In addition to the configuration mentioned above, the back face 23 ofthe transparent substrate of the light-emitting diode allows a metallicfilm to be formed thereon. The metallic film is capable of imparting afunction of reflecting light and a function of heightening thermalconduction to the light-emitting diode side and widening the range ofselection of packaging material as well. The metallic film prefers tocontain a metal having a melting point not exceeding 400° C. As a meansto connect the transparent substrate of the light-emitting diode to thepackage, the soldering or the technique using eutectic bonding can beadopted. This method is most suitable in terms of the exoergic propertybecause the light-emitting diode and the package can be connected via ametal by using this method. Then, by adding a metal for the sake ofconnection to the back face 23 of the light-emitting diode, theassemblage of the light-emitting diode lamp can be facilitated. Inconsideration of the material generally used for the package, theconditions for effecting the connection at a temperature not exceeding400° C. prove to be favorable.

For the metallic film, the use of an AuSn alloy proves to be favorable.The AuSn alloy is used as a eutectic metal and, because the AuSn alloyhaving an Sn content of 20 wt % at the eutectic point has a meltingpoint of about 283° C., proves to be the most suitable material thatallows connection at a low temperature.

As a method for producing the light-emitting diode besides the methoddescribed above, any of the known techniques available for thefabrication of light-emitting diodes may be utilized. Through theprocess consisting of such steps as formation of an ohmic electrode,separation, and inspection and evaluation, the light-emitting diode isfabricated. Further, by having the light-emitting diode incorporated inthe package, such lighting fixture as a lamp can be manufactured.

The light-emitting diode according to the second embodiment of thisinvention is characterized in that a transparent substrate has a firstside face nearly perpendicular to the light-emitting surface of alight-emitting layer at a portion on the side near the light-emittinglayer and a second side face inclined relative to the light-emittingsurface at a portion on the side distant from the light-emitting layer.

The light-emitting diode of this invention prefers to have thisconfiguration for the reason that the configuration enables the lightradiated from the light-emitting layer toward the transparent substrateside to be extracted efficiently to the exterior. To be specific, partof the light radiated from the light-emitting layer toward thetransparent substrate side can be reflected by the first side face andextracted from the second side face. The light reflected by the secondside face can be extracted from the first side face. The synergisticeffect of the first side face and the second side face results inenabling addition to the probability of light extraction.

The light-emitting diode of the second embodiment prefers to limit theangle α formed by the second side face and the surface parallel to thelight-emitting surface within the range of 55 degrees˜80 degrees (referto FIG. 11). By causing the angle to fall in this range, it is madepossible to attain efficient extraction to the exterior of the lightreflected on the bottom part of the transparent substrate.

The light-emitting diode of the second embodiment prefers to have thelength D (in the direction of thickness) of the first side face fall inthe range of 30 μm˜100 μm. By limiting the length of the first side facein this range, it is made possible to heighten the efficiency of lightemission of the light-emitting diode of this invention because the lightreflected on the bottom part of the transparent substrate is efficientlyreturned to the light-emitting surface at the portion of the first sideface and radiated through the main light-extracting surface.

In the configuration of the invention, the first electrode prefers toassume the shape of a lattice. By giving the first electrode this shapeof a lattice, it is made possible to enhance the reliability of thelight-emitting diode of this invention because the shape enables uniforminjection of an electric current to the light-emitting layer.

Then, the light-emitting diode of the second embodiment allows the firstelectrode to be formed of a pad electrode and a linear electrode havinga width not exceeding 10 μm. Owing to the configuration directed towarddecreasing the width of the electrode as described above, it is madepossible to attain impartation of high brightness to the light-emittingdiode of this invention because the area of openings in thelight-extracting surface can be consequently increased.

Further, by forming the first electrode in the shape of a lattice, it ismade possible to enhance the reliability of the light-emitting diode ofthis invention because the lattice allows uniform injection of anelectric current to the light-emitting layer.

The light-emitting diode of the second embodiment prefers to have theperiphery of the second electrode enclosed with a semiconductor layer.By adopting the configuration directed toward surrounding the four sidesof the second electrode with the first electrode as described above, itis made possible to lower the operating voltage because the electriccurrent is allowed to flow easily in four directions.

The light-emitting diode of the second embodiment allows thelight-emitting part to have a structure incorporating a GaP layer andpermits the second electrode to be formed on the GaP layer. The adoptionof this configuration enables manifestation of an effect of lowering theoperating voltage. By having the second electrode formed on the GaPlayer, it is made possible to enable production of an ideal ohmiccontact and lower the operating voltage consequently.

The light-emitting diode of the second embodiment prefers to give thefirst electrode n-type polarity and the second electrode p-typepolarity. The adoption of this configuration brings about an effect ofenhancing brightness. The formation of the first electrode in the p-typepolarity results in deteriorating the diffusion of the electric currentand degrading the brightness. Nevertheless, the formation of the firstelectrode in the n-type polarity results in enhancing the diffusion ofthe electric current and realizing impartation of high brightness to thelight-emitting diode.

The light-emitting diode of the second embodiment prefers to have theinclined face of the transparent substrate formed into a coarsenedsurface. The impartation of the coarsened surface to the inclined faceresults in suppressing the total reflection on the inclined face andenhancing the efficiency of light extraction. The coarsened surface canbe obtained, for example, by a chemical etching with phosphoricacid+hydrochloric acid.

Then, the light-emitting diode of the second embodiment, besides theconfiguration mentioned above and similarly to the light-emitting diodeof the first embodiment, allows a metallic film to be formed on the backface 23 of the transparent substrate of the light-emitting diode.

The light-emitting diode of the second embodiment can be producedutilizing the method available for the production of the light-emittingdiode of the first embodiment.

In this invention, the first side face prefers to be formed by thescribe and break method or the dicing method. By adopting the formermethod of production, it is made possible to lower the cost ofproduction. Specifically, this method of production permits productionof numerous light-emitting diodes and allows reduction of the cost ofproduction because it obviates the necessity of leaving cuttingallowance behind during the separation of chips. The latter methodbrings about an effect of heightening brightness. By adopting thismethod of production, it is made possible to add to the efficiency oflight extraction through the first side face and achieve impartation ofincreased brightness.

By the same token, the second side face prefers to be formed by thedicing method. By adopting this method of production, it is madepossible to bring about an effect of augmenting the yield of production.The first side face and the second side face can be formed usingmethods, such as wet etching, dry etching, scribing and laser processingin combination. Nevertheless, the dicing method that excels in the shapecontrolling property and the productivity proves to be most suitable.

As a method for producing the light-emitting diode besides the methoddescribed above, any of the known techniques available for theproduction of light-emitting diodes may be utilized. Through the processconsisting of such steps as formation of an ohmic electrode, separation,and inspection and evaluation, the light-emitting diode is produced.Further, by having the light-emitting diode incorporated in the package,such lighting fixture as a lamp can be manufactured.

The light-emitting diode according to the third embodiment of thisinvention possesses a configuration in common at large with the secondembodiment of this invention and can be produced by making use of themethod of production of the light-emitting diode of the secondembodiment.

To be specific, the light-emitting diode of the third embodiment isconfigured by causing a transparent substrate to form a first side facenearly perpendicular to the light-emitting surface of a light-emittinglayer at a portion on the side near the light-emitting layer and asecond side face inclined relative to the light-emitting surface at aportion on the side distant from the light-emitting layer and causingthe second side face to be inclined toward the inner side of asemiconductor layer.

The light-emitting diode of the third embodiment, in the configurationof the second embodiment described above, is further characterized byhaving the second electrode formed at the position of a corner on acompound semiconductor layer on the side opposite the first electrode.The expression “the position of a corner on a compound semiconductorlayer” as used herein refers to the parts of the corners at fourportions on the plane of a tetragonal compound semiconductor, forexample. This invention allows the second electrode to be formed in atleast one of the corners located at the four portions. By having thesecond electrode formed at the position mentioned above, it is madepossible to enable impartation of heightened brightness to thelight-emitting diode of this invention because part of the lightradiated from the light-emitting layer to the light-extracting surfacecan be extracted through the side face of the compound semiconductorlayer near the second electrode.

The second electrode can be formed at a position above the inclinedstructure of the second side face. By having the second electrode formedat this position, it is made possible to realize impartation ofheightened brightness because the light-emitting diode of this inventionis enabled to acquire addition to the efficiency of light extraction inthe inclined face.

Now, the light-emitting diode embodying this invention will be describedbelow by reference to the accompanying drawings. In the followingexplanation, the parts appearing in different drawings and fulfillingidentical or equivalent functions will be denoted by like referencenumerals and their descriptions will not be repeated.

Example 1 and Example 2 in the following description are examples morespecifically illustrating the configuration of the light-emitting diodeaccording to the first embodiment Example 3 and Example 4 morespecifically illustrate the light-emitting diodes respectively accordingto the second embodiment and the third embodiment.

Example 1

FIG. 1 and FIG. 2 schematically illustrate a semiconductorlight-emitting diode 10 fabricated in Example 1. FIG. 1 is a plan viewand FIG. 2 is a cross section taken across FIG. 1 along line II-II. FIG.3 is a schematic cross section of the layered structure of asemiconductor epitaxial stacked structure to be used in thesemiconductor light-emitting diode 10 of Example 1 and FIG. 4 is aschematic cross section illustrating a structure resulting from joininga substrate 14 to the semiconductor epitaxial stacked structure of FIG.3.

The semiconductor light-emitting diode 10 fabricated in Example 1 was ared color Light-Emitting Diode (LED) possessing an AlGaInPlight-emitting part 12. It was fabricated by joining an epitaxialstacked structure formed on a semiconductor substrate 11 made of GaAsand the GaP substrate 14.

The light-emitting diode 10 was fabricated by using an epitaxial waferthat was furnished with an epitaxial growth layer 13 composed ofsemiconductor layers sequentially stacked on the semiconductor substrate11 formed of an Si-doped n-type GaAs single crystal possessing a faceinclined by 15° from the (100) face. The epitaxial growth layer 13 wasconfigured by sequentially stacking component semiconductor layers, i.e.an etching stop layer 130A formed of Si-doped n-type(Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, a contact layer 131 formed ofSi-doped n-type GaAs, a lower clad layer 132 formed of Si-doped n-type(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a light-emitting layer 133 formed of20 pairs of undoped (Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P and(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, an upper clad layer 134 formed ofMg-doped p-type (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P and an Mg-doped p-typeGaP layer 135.

In Example 1, the semiconductor layers 130A˜135 were individuallystacked on the semiconductor substrate 11 by the low-pressureMetalOrganic Chemical Vapor Deposition method (MOCVD method) usingtrimethyl aluminum ((CH₃)₃Al), trimethyl gallium ((CH₃)₃Ga) andtrimethyl indium ((CH₃)₃In) as the raw materials for Group III componentelements to give birth to an epitaxial wafer. As the raw material forthe doping with Mg, biscyclopentadiethyl magnesium (bis-(C₅H₅)₂Mg) wasused. As the raw material for the doping with Si, disilane (Si₂H₆) wasused. As the raw material for the Group V component element, phosphine(PH₃) or arsine (AsH₃) was used. The GaP layer 135 was grown at 750° C.and the component semiconductor layers 130A˜134 forming the epitaxialgrowth layer 13 were grown at 730° C.

The etching stop layer 130A had a carrier concentration of about 2×10¹⁸cm⁻³ and a layer thickness of about 0.2 μm. The contact layer 131 had acarrier concentration of about 2×10¹⁸ cm⁻³ and a layer thickness ofabout 0.2 μm. The n-type lower clad layer 132 had a carrierconcentration of about 8×10¹⁷ cm⁻³ and a layer thickness of about 2 μm.The undoped light-emitting layer 133 had a layer thickness of 0.8 μm.The p-type upper clad layer 134 had a carrier concentration of about2×10¹⁷ cm⁻³ and a layer thickness of about 1 μm. The GaP layer 135 had acarrier concentration of about 3×10¹⁸ cm⁻³ and a layer thickness ofabout 9 μm.

The p-type GaP layer 135 was mirror finished by subjecting a regionthereof reaching a depth of about 1 μm from the surface to polishing. Bythe mirror finishing, the surface of the p-type GaP layer 135 was givenroughness of 0.18 nm in the root-mean-square (rms) value.

Meantime, the n-type GaP substrate 14 to be applied to themirror-finished surface of the p-type GaP layer 135 was prepared. Tothis GaP substrate 14 for the application, Si was added till the carrierconcentration reached about 1×10¹⁷ cm⁻³. A single crystal having asurface orientation of (111) was used. The GaP substrate 14 for theapplication had a diameter of 50 mm and a thickness of 250 μm. This GaPsubstrate 14 was given a specular surface by polishing and finished withcoarseness of 0.12 nm in the rms value prior to being joined to thep-type Gap layer 135.

The GaP substrate 14 and the epitaxial wafer were carried in an ordinarysemiconductor material-applying device and the device was evacuated tilla vacuum of 3×10⁻⁵ Pa. Then, the surfaces of the GaP substrate 14 andthe epitaxial wafer were deprived of adhering contaminant by beingexposed to an accelerated Ar beam by way of treatment prior to beingjoined. Thereafter, they were joined in a vacuum at room temperature.

Next, from the epitaxial wafer so joined, the semiconductor substrate 11was selectively removed with an ammonia-based etchant. Thereafter, theetching stop layer 130A was removed with hydrochloric acid.

An AuGeNi alloy was deposited till a thickness of 0.2 μm on the surfaceof the contact layer 131 by the vacuum evaporation method to form ann-type ohmic electrode on the surface of the contact layer 131. Then-type ohmic electrode was subjected to patterning by the use of anordinary photolithographic means to form a first electrode 15.Thereafter, the part of the contact layer 131 other than theelectrode-forming part was removed.

Next, the semiconductor layers 132˜134 inclusive of the light-emittinglayer 133 in the region for forming the p-electrode were selectivelyremoved to expose the GaP layer 135. On the surface of the GaP layer135, the metal materials for AuBe and Au were deposited by the vacuumevaporation method till AuBe reached a thickness of 0.2 μm and Aureached a thickness of 1 μm to form a p-type ohmic electrode. At thattime, the light-emitting layer 133 had an area of 0.72 mm². By furthersubjecting the metal materials to a heat treatment at 450° C. for 10minutes, thereby alloying them, the first electrode 15 as alow-resistance n-type ohmic electrode and a second electrode 16 as ap-type ohmic electrode were formed.

Thereafter, Au was deposited till a thickness of 1 μm by the vacuumevaporation method on the surfaces of the first electrode and the secondelectrode to form a bonding pad 17 on the ohmic electrodes. Further, thepart excluding the bonding pad 17 was covered with a protective filmformed of an SiO₂ film 0.3 μm in thickness.

From the back surface 23 of the GaP substrate 14, a V-shaped groove wasinserted by the use of a dicing saw till the angle 20 of the inclinedface reached 15 degrees and the length of the second side face 22reached about 180 μm. Then, the back surface 23 of the GaP substrate 14was subjected to a coarsening treatment with hydrochloric acid.

Next, cuts were inserted into the epitaxial wafer at intervals of 1 mmfrom the first surface side by the use of a dicing saw to manufacturechips. The first side face 12 was formed in a length of about 80 μmnearly perpendicularly to the light-emitting layer 133.

The broken layer and the contaminant caused by dicing were removed witha mixed liquid of sulfuric acid and hydrogen peroxide to fabricate thesemiconductor light-emitting diode 10. The back surface 23 of thesemiconductor light-emitting diode 10 had an area of 0.8 mm².

The semiconductor light-emitting diode 10 fabricated as described abovewas used as an LED chip 42 and a semiconductor Light-Emitting Diode lamp(LED lamp) 1 was assembled as illustrated schematically in FIG. 8 andFIG. 9. This LED lamp 1 was fabricated by fixing and mounting the LEDchip 42 with silver paste on a mounting substrate 45, wire-bonding then-type ohmic electrode 15 of the LED chip 42 to an n-electrode terminal43 installed on the first surface of the mounting substrate 45 and thep-type ohmic electrode 16 to a p-electrode terminal 44 severally with agold wire 46, and then sealing the joined parts with ordinary epoxyresin 41. Incidentally, aluminum nitride possessing a good exoergicproperty was used for the basic body of the mounting substrate 45.

When an electric current was made to pass between the n-type and p-typeohmic electrodes 15 and 16 via the n-electrode terminal 43 and thep-electrode terminal 44 installed on the first surface of the mountingsubstrate 45, the LED lamp 1 emitted a red color light having a mainwavelength of 620 nm. The forward voltage (Vf) during the flow of anelectric current of 500 mA in the forward direction reached about 2.4 V,a magnitude reflecting excellent ohmic properties of the ohmicelectrodes 15 and 16. The intensity of the light emitted when theforward current was set at 500 mA was enabled to reach such highbrightness of 5500 mcd by reflecting the fact that the structure of thelight-emitting part of high efficiency of light emission and the removalof the broken layer taking place during the reduction of the epitaxialwafer into chips resulted in enhancing the efficiency of extraction oflight to the exterior.

Example 2

A semiconductor light-emitting diode 10 of Example 2 possessing the samestructure as in Example 1 while having a metal layer 24 of an AuSneutectic (melting point 283° C.) formed on the back surface asillustrated in FIG. 5 was fabricated.

A semiconductor Light-Emitting Diode lamp (LED lamp) 1 possessing thestructure illustrated schematically in FIG. 8 and FIG. 9 was assembledby following the same procedure as in the use of the semiconductorlight-emitting diode 10 of Example 1 while using the semiconductorlight-emitting diode 10 of Example 2 as an LED chip 42 and using AuSn inthe place of the Ag paste.

The semiconductor light-emitting diode lamp 1 that was manufactured byusing the semiconductor light-emitting diode 10 of Example 2 wasevaluated in the same manner as in Example 1. The results are shown inTable 1 below. The forward voltage (Vf) during the flow of an electriccurrent of 500 mA in the forward direction was 2.4 V. The intensity oflight emission was enabled to reach a high brightness of 6430 med byreflecting the fact that the exoergic property was further enhanced andthe absorption of light by the Ag paste was eliminated.

Comparative Example 1

A semiconductor light-emitting diode 10A of Comparative Example 2illustrated in FIG. 6 was fabricated by following the procedure using adicing saw similarly to Example 1 while changing the shape of the sideface of the GaP substrate 14. The first side face was nearlyperpendicular and had a length of 10 μm and the second side face had anangle of 30 degrees and a length of 300 μm. The back surface assumed anarea of 0.5 mm². The light-emitting layer had an area of 0.72 mm²similarly to Example 1. A semiconductor Light-Emitting Diode lamp (LEDlamp) possessing the structure illustrated schematically in FIG. 8 andFIG. 9 was assembled by following the same procedure as in the use ofthe semiconductor light-emitting diode 10 of Example 1 while using thesemiconductor light-emitting diode 10A of Comparative Example 1 as theLED chip 42.

The semiconductor light-emitting diode lamp using the semiconductorlight-emitting diode 10A of Comparative Example 1 was subjected to thesame evaluation as in the case of Example 1. The results are shown inTable 1 below. The forward voltage (Vf) during the flow of an electriccurrent of 500 mA in the forward direction was 2.4 V. The intensity oflight emission of the semiconductor light-emitting diode lamp ofComparative Example 1 was only 3290 mcd in brightness because thesemiconductor light-emitting diode 10A of Comparative Example 1 had aback surface of small area and revealed deficiency in heat radiation.

Comparative Example 2

A semiconductor light-emitting diode 10B of Comparative Example 2 devoidof an inclined face was fabricated (FIG. 7) by following the procedureusing a dicing saw similarly to Example 1 while changing the shape ofthe side face of the GaP substrate 14. The back surface had an area of0.9 mm². The light-emitting layer had an area of 0.72 mm² similarly toExample 1. A semiconductor Light-Emitting Diode lamp (LED lamp)possessing the structure illustrated schematically in FIG. 8 and FIG. 9was assembled by following the same procedure as in the use of thesemiconductor light-emitting diode 10 of Example 1 while using thesemiconductor light-emitting diode 10B of Comparative Example 2 as theLED chip 42.

The semiconductor light-emitting diode lamp using the semiconductorlight-emitting diode 10B of Comparative Example 2 was subjected to thesame evaluation as in the case of Example 1. The results are shown inTable 1 below. The forward voltage (Vf) during the flow of an electriccurrent of 500 mA in the forward direction was 2.4 V. The intensity oflight emission was only 4270 mcd in brightness because the efficiency oflight extraction was slightly low owing to the absence of an inclinedface.

TABLE 1 First Second Area Brightness Forward side face side face (mm²)(mcd) Voltage (V) Angle of Length Angle of Length Light-emitting Back IF= IF = IF = IF = inclination (μm) inclination (μm) layer surface 100 mA500 mA 100 mA 500 mA Ex. 1 0 80 15 180 0.75 0.8 1150 5500 2 2.4 Ex. 2 080 15 180 0.75 0.8 1280 6430 2 2.4 Comp. 0 10 30 300 0.75 0.5 1190 32902 2.4 Ex. 1 Comp. 0 250 0 — 0.75 0.9 860 4270 2 2.4 Ex. 2

Example 3

As another concrete example of the second embodiment, the light-emittingdiode according to Example 3 will be described below by reference to theaccompanying drawings.

FIG. 10 and FIG. 11 illustrate the semiconductor light-emitting diode 10of Example 3; FIG. 10 is a plan view and FIG. 11 is a cross sectiontaken across FIG. 10 along line XI-XI. FIG. 12 is a schematic crosssection of the layered structure of the semiconductor epitaxial stackedstructure used in the light-emitting diode 10 of Example 3 and FIG. 13is a schematic cross section illustrating a structure resulting fromjoining the GaP substrate 14 to the semiconductor epitaxial stackedstructure of FIG. 12.

The semiconductor light-emitting diode 10 of Example 3 was a red colorLight-Emitting Diode (LED) possessing an AlGaInP light-emitting part 12and was fabricated by joining an epitaxial stacked structure installedon a semiconductor substrate 11 made of GaAs to the GaP substrate 14.

The light-emitting diode 10 of Example 3 was fabricated by using anepitaxial wafer that was furnished with an epitaxial growth layer 13composed of semiconductor layers sequentially stacked on thesemiconductor substrate 11 formed of an Si-doped n-type GaAs singlecrystal possessing a surface inclined by 15° from the (1000) face. Theepitaxial growth layer 13 was configured by sequentially stackingcomponent semiconductor layers, i.e. a buffer layer 130B formed of anSi-doped n-type GaAs, a contact layer 131 formed of Si-doped n-type(Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, a lower clad layer 132 formed ofSi-doped n-type (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P, a light-emittinglayer 133 formed of 20 pairs of undoped(Al_(0.2)Ga_(0.8))_(0.5)In_(0.5)P and (Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P,an upper clad layer 134 formed of Mg-doped p-type(Al_(0.7)Ga_(0.3))_(0.5)In_(0.5)P and an Mg-doped p-type GaP layer 135.

The semiconductor layers 130B˜135 were individually stacked by thelow-pressure MetalOrganic Chemical Vapor Deposition method (MOCVDmethod) in the same manner as when the semiconductor layers 130A˜135forming the epitaxial growth layer 13 of Example 1 were stacked.Consequently, an epitaxial wafer to be used in Example 3 was formed.

The GaAs buffer layer 130B had a carrier concentration of about 2×10¹⁸cm⁻³ and a layer thickness of about 0.2 μm. The contact layer 131 had acarrier concentration of about 2×10¹⁸ cm⁻³ and a layer thickness ofabout 1.5 μm. The n-clad layer 132 had a carrier concentration of about8×10¹⁷ cm⁻³ and a layer thickness of about 1 μm. The undopedlight-emitting layer 133 had a thickness of 0.8 μm. The p-clad layer 134had a carrier concentration of about 2×10⁻³ cm⁻³ and a layer thicknessof 1 μm. The GaP layer 135 had a carrier concentration of about 3×10¹⁸cm⁻³ and a layer thickness of 9 μm.

The p-type GaP layer 135 had a region reaching a depth of about 1 μmfrom the first surface polished till a specular finish. By the specularfinish, the surface of the p-type GaP layer 135 was made to reach aroughness of 0.18 nm.

Meantime, the n-type GaP substrate 14 to be mounted on the surface ofmirror finish of the p-type GaP layer 135 was prepared. The mounting GaPsubstrate 14 needed for the fabrication of the light-emitting diode 10of Example 3 was prepared in the same manner as that was used in thefabrication of the light-emitting diode 10 of Example 1.

The GaP substrate 14 and an epitaxial wafer were carried into anordinary device for mounting a semiconductor material and the interiorof this device was evacuated till a vacuum of 3×10⁻⁵ Pa. Thereafter, theGaP substrate 14 disposed inside the device that had expelled membersmade of a carbonaceous material with a view to avoiding contaminationwith carbon was heated in the vacuum to a temperature of about 800° C.while the surface of the GaP substrate 14 was exposed to Ar ionsaccelerated to an energy of 800 eV. As a result, a joining layer 141having a nonstoichiometric composition was formed on the surface of theGap substrate 14. Subsequent to the formation of the joining layer 141,the radiation of the Ar ions was stopped and the GaP substrate 14 wascooled to room temperature.

Next, the first surfaces of both the GaP substrate 14 furnished in thesurface region with the joining layer 141 made of a nonstoichiometriccomposition and the GaP layer 135 were exposed over a period of threeminutes to an Ar beam neutralized by collision with electrons.Thereafter, inside the mounting device maintained in a vacuum, thesurfaces of the GaP layer 135 and the GaP substrate 14 were overlappedand given such a load as to exert a pressure of 20 g/cm² on each of thesurfaces and both the substrate and the layer were consequently joinedat room temperature (refer to FIG. 13). When the joined wafers wereextracted from the vacuum chamber of the mounting device and theirinterface was analyzed, it was found that the joining layer 141 ofGa_(0.6)P_(0.4) having a nonstoichiometric composition was formed in theinterface. The joining layer 141 had a thickness of about 3 nm, anoxygen atom concentration of 7×10¹⁸ cm⁻³, a magnitude found by theordinary method of SIMS, and a carbon atom concentration of 9×10¹⁸ cm⁻³.

Next, the semiconductor substrate 11 and GaAs buffer layer 130B wereselectively removed from the joined wafers with an ammonia-basedetchant.

For the purpose of forming the ohmic electrode 15 as the first electrodeon the surface of the contact layer 131, first an AuGeNi alloy wasdeposited in a thickness of 0.5 μm, Pt was deposited in a thickness of0.2 μm, and Au was deposited in a thickness of 1 μm by the vacuumevaporation method to produce an n-type ohmic electrode. Then, thisn-type ohmic electrode was subjected to patterning by the ordinary meansof photolithography to form the first electrode 15.

Next, the semiconductor layers 131˜134 in the region for forming thep-electrode were selectively removed to expose the GaP layer 135. On thesurface of the GaP layer 135, AuBe and Au were deposited in respectivethicknesses of 0.2 μm and 1 μm to form a p-type ohmic electrode bysubjecting their metallic materials to the method of vacuum evaporation.Further, by having these electrodes alloyed by a heat treatmentperformed at 450° C. for 10 minutes, the first electrode 15 as alow-resistance n-type ohmic electrode and the second electrode 16 as ap-type ohmic electrode were formed (refer to FIG. 10 and FIG. 11).

Next, from the back surface of the GaP substrate 14, a V-shaped groovewas inserted by using a dicing saw so as to give an angle of 70° (theangle α formed by the second side face 143 and the surface parallel tothe light-emitting surface) to an inclined face and a size of 80 μm tothe first side face 142.

Then, from the first surface side, cuts were inserted at intervals of350 μm to produce chips. The broken layer and the contaminant caused bythe dicing were etched and removed by using a mixed liquid of sulfuricacid and hydrogen peroxide to complete fabrication of the semiconductorlight-emitting diode (chips) 10.

By using as the LED chips 42 the semiconductor light-emitting diodes 10that had been fabricated as described above, the semiconductorLight-Emitting Diode lamp (LED lamp) 1 was assembled as illustratedschematically in FIG. 14 and FIG. 15. This LED lamp 1 was manufacturedby fixing and mounting the LED chip 42 on the mounting substrate 42 withsilver (Ag) paste, wire-bonding the n-type ohmic electrode 15 of the LEDchip 42 over the n-electrode terminal 43 disposed on the first surfaceof the mounting substrate 45 and the p-type ohmic electrode 16 over thep-electrode terminal 44 respectively with the gold wire 46, andthereafter sealing the joined faces with the ordinary epoxy resin 41.Incidentally, aluminum nitride possessing an excellent exoergic propertywas used as the base material for the mounting substrate 45. The ohmicelectrode 15 comprises a pad electrode 15 a and a linear electrode 15 b.

When an electric current was made to pass between the n-type and p-typeohmic electrodes 15 and 16 via the n-electrode terminal 43 and thep-electrode terminal 44 installed on the surface of the mountingsubstrate 45, a red color light having a main wavelength of 620 nm wasemitted. The forward voltage (Vf) that occurred during the passage of anelectric current of 20 mA in the forward direction reached about 1.95 V,a magnitude reflecting the good ohmic properties of the ohmic electrodes15 and 16. The intensity of light emission that occurred when theforward electric current was set at 20 mA reached high brightness of 600mcd, a magnitude reflecting the structure of the light-emitting parthaving a high efficiency of light emission and the enhancement of theefficiency of extraction to the exterior owing to the removal of thebroken layer taking place during the cutting into chips.

Example 4

Now, as a still another concrete example of the third embodiment, thelight-emitting diode according to Example 4 will be described below byreference to the drawings.

The semiconductor light-emitting diode 10 of Example 4 was a red colorLight-Emitting Diode (LED) furnished with an AlGaInP light-emitting part12 and was fabricated by bonding an epitaxial stacked structure disposedon the semiconductor substrate 11 made of GaAs to the GaP substrate 14(refer to FIG. 16 and FIG. 17). FIG. 16 is a plan view thereof and FIG.17 is a cross section taken across FIG. 16 along line XVII-XVII.

The semiconductor light-emitting diode 10 of Example 4 was fabricated byusing the same semiconductor epitaxial stacked structure as used in thelight-emitting diode of Example 3 and following the same method ofproduction as used in Example 3.

The light-emitting diode 10 of Example 4 was constructed similarly tothe light-emitting diode 10 of Example 3, except the second electrode 16was formed at the position of a corner on the compound semiconductorlayer on the side opposite the first electrode 15 and the electrodes 15and 16 were disposed in this manner.

That is, the light-emitting diode 10 of Example 4 was so constructedthat the side face of the GaP substrate 14 serving as a transparentsubstrate formed a first side face 142 nearly perpendicular to thelight-emitting surface of the light-emitting layer 133 at the portion onthe side near the light-emitting layer 133 and a second side face 143inclined to the light-emitting surface at the portion on the sidedistant from the light-emitting layer 133 and the second side face 143was inclined with an angle α toward the inner side of the semiconductorlayer.

The semiconductor Light-Emitting Diode lamp (LED lamp) 1 possessing astructure illustrated schematically in FIG. 14 and FIG. 15 wasfabricated by using as the LED chips 42 the semiconductor light-emittingdiode 10 of Example 4 and following the same procedure as in the case ofusing the semiconductor light-emitting diode 10 of Example 3.

When an electric current was made to pass between the n-type and p-typeohmic electrodes via the n-electrode terminal 43 and the p-electrodeterminal 44 installed on the surface of the mounting substrate 45, a redcolor light having a main wavelength of 620 nm was emitted. The forwardvoltage (Vf) that occurred during the passage of an electric current of20 mA in the forward direction reached about 2.10 V, a magnitudereflecting the good ohmic properties of the ohmic electrodes 15 and 16.The intensity of light emission that occurred when the forward electriccurrent was set at 20 mA reached high brightness of 800 mcd, a magnitudereflecting the structure of the light-emitting part having a highefficiency of light emission and the enhancement of the efficiency ofextraction to the exterior owing to the removal of the broken layertaking place during the cutting into chips.

Comparative Example 3

A semiconductor light-emitting diode 10C of Comparative Example 3illustrated in FIG. 18 and FIG. 19 was fabricated by joining thetransparent substrate 14 to the semiconductor layer in accordance withthe same method of production as in Example 3, except the second sideface of the transparent substrate 14 was formed perpendicularly to thelight-emitting part 13 as illustrated in FIG. 19. Incidentally, ann-type ohmic electrode 15 c formed on the surface of the contact layer131 was not shaped in a reticular pattern as shown in FIG. 18 and ap-type ohmic electrode 16 c formed on the surface of the GaP layer 135was so shaped as to have part of the periphery thereof covered with acompound semiconductor layer.

The semiconductor light-emitting diode of Comparative Example 3 had beenobtained as a chip identical in size with the diode of Example 3.Subsequent to the cutting, the broken layer and the contaminant producedby the work of dicing were etched and removed with a mixed liquid ofsulfuric acid and hydrogen peroxide.

A semiconductor Light-Emitting Diode lamp (LED lamp) having a structureillustrated schematically in FIG. 14 and FIG. 15 was assembled byfollowing the procedure of using the semiconductor light-emitting diode10 in Example 3 except using the semiconductor light-emitting diode 10Cof Comparative Example 3.

The LED lamp using the semiconductor light-emitting lamp 10C ofComparative Example 3, when an electric current was passed between then-type and p-type ohmic electrodes 15 c and 16 c via the n-electrodeterminal 43 and the p-electrode terminal 44 disposed on the surface ofthe mounting substrate 45, emitted a red color light having a mainwavelength of 620 nm. The forward voltage (Vf) occurring during thepassage of an electric current of 20 mA in the forward direction reachedabout 2.30 V. The intensity of light emission that occurred when theforward electric current was set at 20 mA barely reached brightness of200 mcd.

INDUSTRIAL APPLICABILITY

The light-emitting diode of this invention is characterized by excellingin the exoergic property and exhibiting high brightness and, owing tothe superior exoergic property, can be used with a large electric power.Further, the light-emitting diode of this invention is capable ofemitting light in red color, orange color, yellow color or yellowishgreen color.

1. A light-emitting diode possessing a transparent substrate and alight-emitting layer made of a compound semiconductor, wherein an area(A) of a light-extracting surface having formed thereon a firstelectrode and a second electrode differing in polarity from the firstelectrode, an area (B) of the light-emitting layer formed approximate tothe light-extracting surface, and an area (C) of a back surface of thelight-emitting diode falling on a side opposite a side for forming thefirst electrode and the second electrode are so related as to satisfy arelation of formula A>C>B, the transparent substrate possesses a sideface comprising a first side face approximate to the light-emittinglayer, and a second side face approximate to a back surface of thetransparent substrate, and the first side face has an angle ofinclination, with respect to a first direction being substantiallyperpendicular to the back surface of the transparent substrate, smallerthan an angle of inclination of the second side face, with respect tothe first direction.
 2. A light-emitting diode according to claim 1,wherein the light-emitting layer has a composition of formula(Al_(X)Ga_(1-X))_(Y)In_(1-Y)P; wherein 0≦X≦1, 0≦Y≦1, and the transparentsubstrate has a heat transfer coefficient not less than 100 W/m·k.
 3. Alight-emitting diode according to claim 1, wherein the first side faceis perpendicular to a top surface of the light-emitting layer, and thesecond side face is slanted with respect to the first direction.
 4. Alight-emitting diode according to claim 1, wherein the angle ofinclination of the second side face is between 10 degrees and 30degrees.
 5. A light-emitting diode according to claim 1, wherein theangle of inclination of the second side face is between 10 degrees and20 degrees.
 6. A light-emitting diode according to claim 1, wherein thefirst side face has a length between 50 μm and 100 μm and the secondside face has a length between 100 μm and 250 μm.
 7. A light-emittingdiode according to claim 1, wherein the transparent substrate is made ofgallium phosphide (GaP).
 8. A light-emitting diode according to claim 1,wherein the transparent substrate has a back surface that is a coarsenedsurface capable of scattering light.
 9. A light-emitting diode accordingto claim 8, wherein the transparent substrate is a GaP substrate theback surface thereof results from treatment of the GaP substrate withhydrochloric acid.
 10. A light-emitting diode according to claim 1,wherein the transparent substrate has a back surface having a metal filmformed thereon.
 11. A light-emitting diode according to claim 10,wherein the metal film on the back surface of the transparent substratecontains a metal having a melting point of 400° C. or less.
 12. Alight-emitting diode according to claim 10, wherein the metal film ismade of an AuSn alloy.
 13. A light-emitting diode according to claim 1,wherein the light-emitting diode is used with an electric power not lessthan 1.5 W and the area of the back surface thereof is not less than 0.6mm².
 14. A light-emitting diode according to claim 1, wherein the firstand second side faces of the transparent substrate are those formed bythe dicing method.